Generally, in a turbine such as a gas turbine and a steam turbine, a seal device for reducing a leakage amount of a fluid that flows from the high-pressure side toward the low-pressure side is disposed between the outer peripheral surface of a rotor and the tip of a stator.
As a type of such seal device, known is a thin-plate seal structure having a plurality of thin plates (leafs) arranged in the circumferential direction of the rotor in a multiple-layered fashion, as disclosed in Patent Documents 1 to 3. Normally, the thin plates are in contact with the rotor while the turbine is stopped, but the thin-plate tip portions separate from the rotor peripheral surface while the turbine is in operation, so that the thin plates are in a non-contact state with the rotor or in a state in which the non-contact state and the contact state are mixed in time series. As compared to the labyrinth structure, the thin-plate seal structure is advantageous in that the leakage amount of fluid is small thanks to smaller clearance, as well as that abrasion of thin plates is less likely to occur thanks to the thin plates being in the non-contact state with the rotor more often, thus having a longer seal lifetime.